Area Forecast Discussion
Issued by NWS Juneau, AK
Issued by NWS Juneau, AK
680 FXAK67 PAJK 271346 AFDAJK Southeast Alaska Forecast Discussion National Weather Service Juneau AK 546 AM AKDT Sat Apr 27 2024 .SHORT TERM...Rain begins returning to the panhandle as a system moves in, bringing chances of precip through the weekend, though the upcoming week will see increasing chances of drier weather past Monday. Satellite and radar imagery depict cloud cover moving back into the panhandle from S to N, with a low level cloud deck moving through the S panhandle as of the time of writing. This will cap high temperatures in the southern panhandle, though initially clear skies in the N half of the area will enable high temperatures to climb into the upper 50s for this area before increasing cloud cover brings an end to the warm weather. Aloft, a broad trough in the upper levels stretches from the western Bering Sea to Haida Gwaii as of the time of writing. While the primary upper level low is located in the vicinity of the Aleutian Islands, the low`s corresponding fronts are occluding, and cyclogenesis has begun on the opposite side of the Gulf of AK. Aided by divergence aloft on the lee side of the upper level trough the surface reflection of this newly developing low will move north past Haida Gwaii and into the Eastern Gulf through Saturday and Sunday. Past this point, the interaction between the two lows (Fujiwhara Effect), will see the low currently near the Aleutians, by this point substantially weaker, race off to the SE, with the currently developing low retrograding around its own axis before heading back S. Before the developing low departs however, it will bring rain across SE AK. Frontogenesis along the E flank of the developing low will see an initial push of showers into the southern half of the panhandle through Saturday morning, before the primary frontal band itself advances N through the panhandle, reaching into the Icy Strait Corridor northward Saturday night. While there has been some question on how much precipitation will actually manage to make its way through the dry air which has been entrenching itself in SE AK, moisture transport is looking increasingly likely be sufficient to overcome this limitation. Still think that precip totals will be fairly limited, with the greatest QPF totals still progged for the southern panhandle, but almost all of the area will likely see at least some precip - though it is possible that the current totals for Skagway and Haines could be on the generous side. The exception will be Yakutat, which will likely see precip stay more on the low side with this particular system. Maritime winds will see strong small craft conditions across the southern gulf which will successfully push into the southern inner channels through Saturday. Otherwise, the winds in many of the inner channels will be caught between two competing forces - pressure gradient force encouraging N flow, and synoptic flow encouraging S flow. At this time, think that barring the southern channels, N flow will largely win out until the primary frontal band arrives, which should - for a time - be able to overcome the pressure gradient force and bring a surge of S winds into the other inner channels. For additional details, see the marine discussion. Primary changes made to the forecast were to refine the timing of the frontal band associated with the developing low, as well as wind directions in the inner channels as the pressure gradient force and synoptic scale flow pattern contrast each other. Increased QPF across the Icy Strait Corridor somewhat as the system arrives, though still do not expect anything too substantial from this system. .LONG TERM.../Sunday through Tuesday night/...A triple point low will have developed over the eastern Gulf of Alaska and on an existing frontal boundary by Sunday. The small craft intensity surface winds circulating about this low will have already peaked by that time and precipitation associated with the front will be focused primarily over the southern half of the Panhandle with rain likely as far north as Tenakee Springs and Angoon. The low itself will pinwheel over the southeastern Gulf before ejecting southeast and out of the forecast area late Sunday night or early Monday. As this happens, shower activity will diminish from north to South, leaving scattered to isolated shower activity through Monday night and a high probability of dry weather and diminishing cloud cover for Tuesday. The pressure gradient over the inner channels will be quite weak, so winds will be minimal once the low tracks off to the southeast. Daytime highs ranging from the upper 50s to lower 60s, but overnight lows are still getting down close to or slightly below freezing. && .AVIATION...Conditions this morning are a split depending on your location in the panhandle. Most locations across the northern panhandle are reporting VFR conditions with the exception of Yakutat which is reporting half mile and fog this morning at the time of writing. Meanwhile, the southern panhandle is slowly being enveloped by an advancing low cloud deck that is dropping conditions down to MVFR and IFR. This layer is expected to expand north during the day bringing lower CIGs to more areas throughout the day. LLWS is expected to increase across the southern panhandle towards the latter half of the TAF period as winds across the area increase. && .MARINE... Winds increase a low moves in, with 25 to 30 knot winds lifting into the southern waters Saturday. South of Cross Sound and Frederick Strait, expect 8 to 15 ft developing seas, with the highest significant heights south of Cape Decision and west coast of Prince of Wales. Seas become a fresh southwest swell Sunday, with significant heights diminishing through Monday. && .AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...None. MARINE...Small Craft Advisory for PKZ035-036-641>643-661>664. && $$ SHORT TERM...GFS LONG TERM....Fritsch AVIATION...SF MARINE...AP Visit us at http://www.weather.gov/Juneau